Method for steering a smart antenna for a WLAN using a periodic re-scan

Abstract

A smart antenna steering algorithm performs a periodic re-scan at an end of a sustained use period and before a next sustained use period. During a sustained use period, a re-scan of the other antenna beams is not performed. The periodic re-scan is performed on alternate antenna beams that were selected when the preferred antenna beam was selected. The steering algorithm monitors a quality metric of the alternate antenna beams as well as a quality metric for the preferred antenna beam. If the quality metric of the preferred antenna beam is less than the quality metrics of anyone of the alternate antenna beams, then the alternate antenna beam corresponding to the quality metric having a higher value is selected for the next sustained use period.

1. A method for operating a client station in a wireless local area network (WLAN) communication system comprising an access point, the client station comprising an antenna steering algorithm and a smart antenna responsive to the antenna steering algorithm for selecting one of a plurality of antenna beams, the method comprising:
 selecting a preferred antenna beam and at least one alternate antenna beam; 
 exchanging data with the access point using the preferred antenna beam during a sustained use period during which a re-scan of the other antenna beams is not performed; 
 at an end of the sustained use period and before a next sustained use period, calculating a quality metric of exchanged data for the preferred antenna beam and for each alternate antenna beam, the calculating comprising
 determining at least one link quality metric (LQM) of the exchanged data for the preferred antenna beam, 
 determining a signal quality metric (SQM) of the exchanged data for the preferred antenna beam, and 
 combining the at least one LQM and the SQM for calculating the quality metric for the preferred antenna beam, and 
 repeating the determining and combining for calculating an alternate quality metric for each alternate antenna beam; 
 
 comparing the quality metric for the preferred antenna beam to the alternate quality metrics for the alternate antenna beams; and 
 if the quality metric is less than at least one of the alternate quality metrics, then selecting the alternate antenna beam corresponding to the at least one alternate quality metric having a higher value to continue exchanging data with the access point within the next sustained use period. 
 
   
   
     2. A method according to  claim 1  wherein if there is a plurality of alternate quality metrics greater than the quality metric for the preferred antenna beam, then the selected alternate antenna beam corresponds to the alternate antenna beam having the highest alternate quality metric. 
   
   
     3. A method according to  claim 2  further comprising selecting the alternate antenna beam having the next highest alternate quality metric as a new alternate antenna beam. 
   
   
     4. A method according to  claim 1  wherein the alternate antenna beam comprises an omni-directional beam. 
   
   
     5. A method according to  claim 1  wherein the at least one LQM is based upon at least one estimate of a frame error rate (FER) of the exchanged data. 
   
   
     6. A method according to  claim 1  wherein the at least one LQM comprises a downlink LQM and an uplink LQM. 
   
   
     7. A method according to  claim 6  wherein a weighting factor is used when combining the downlink LQM and the uplink LQM. 
   
   
     8. A method according to  claim 6  wherein the client station comprises a media access control (MAC) layer including a plurality of frame counters for estimating frame error rates of the exchanged data; and wherein a first set of counters is used for determining the downlink LQM and a second set of counters is used for determining the uplink LQM. 
   
   
     9. A method according to  claim 1  wherein the at least one LQM is based upon a transfer rate of the exchanged data for the corresponding antenna beam. 
   
   
     10. A method according to  claim 1  wherein the at least one LQM is based upon at least one of a throughput and a data rate of the exchanged data for the corresponding antenna beam. 
   
   
     11. A method according to  claim 1  wherein the SQM is based upon a received signal strength indicator (RSSI) of the exchanged data. 
   
   
     12. A method according to  claim 1  wherein a weighting factor is used when combining the LQM and the SQM. 
   
   
     13. A method according to  claim 1  wherein the plurality of antenna beams comprise a plurality of directional beams and an omni-directional beam. 
   
   
     14. A client station for operating in a wireless local area network (WLAN) communication system comprising an access point, the client station comprising:
 a switched beam antenna for generating a plurality of antenna beams; 
 a beam switching unit coupled to said switched beam antenna for selecting a preferred antenna beam and at least one alternate antenna beam; 
 a transceiver coupled to said beam switching unit for exchanging data with the access point via the preferred antenna beam during a sustained use period during which a re-scan of the other antenna beams is not performed; and 
 an antenna steering algorithm module for running an antenna steering algorithm, and at an end of the sustained use period and before a next sustained use period, calculating a quality metric of exchanged data for the preferred antenna beam and for each alternate antenna beam, the calculating comprising
 determining at least one link quality metric (LQM) of the exchanged data for the preferred antenna beam, 
 determining a signal quality metric (SQM) of the exchanged data for the preferred antenna beam, and 
 combining the at least one LQM and the SQM for calculating the quality metric for the preferred antenna beam, and 
 repeating the determining and combining for calculating an alternate quality metric for each alternate antenna beam; 
 
 said antenna steering algorithm module comparing the quality metric for the preferred antenna beam to the alternate quality metrics for the alternate antenna beams, and if the quality metric is less than at least one of the alternate quality metrics, then selecting the alternate antenna beam corresponding to the at least one alternate quality metric having a higher value to continue exchanging data with the access point within the next sustained use period. 
 
   
   
     15. A client station according to  claim 14  wherein if there is a plurality of alternate quality metrics greater than the quality metric for the preferred antenna beam, then the selected alternate antenna beam corresponds to the alternate antenna beam having the highest alternate quality metric. 
   
   
     16. A client station according to  claim 15  further comprising selecting the alternate antenna beam having the next highest alternate quality metric as a new alternate antenna beam. 
   
   
     17. A client station according to  claim 14  wherein the alternate antenna beam comprises an omni-directional beam. 
   
   
     18. A client station according to  claim 14  wherein the at least one LQM is based upon at least one estimate of a frame error rate (FER) of the exchanged data. 
   
   
     19. A client station according to  claim 14  wherein the at least one LQM comprises a downlink LQM and an uplink LQM. 
   
   
     20. A client station according to  claim 19  wherein a weighting factor is used when combining the downlink LQM and the uplink LQM. 
   
   
     21. A client station according to  claim 19  wherein the client station comprises a media access control (MAC) layer including a plurality of frame counters for estimating frame error rates of the exchanged data; and wherein a first set of counters is used for determining the downlink LQM and a second set of counters is used for determining the uplink LQM. 
   
   
     22. A client station according to  claim 14  wherein the at least one LQM is based upon a transfer rate of the exchanged data for the corresponding antenna beam. 
   
   
     23. A client station according to  claim 14  wherein the at least one LQM is based upon at least one of a throughput and a data rate of the exchanged data for the corresponding antenna beam. 
   
   
     24. A client station according to  claim 14  wherein the SQM is based upon a received signal strength indicator (RSSI) of the exchanged data. 
   
   
     25. A client station according to  claim 14  wherein a weighting factor is used when combining the LQM and the SQM. 
   
   
     26. A client station according to  claim 14  wherein the plurality of antenna beams comprise a plurality of directional beams and an omni-directional beam.